Vaccination of humans and animals against various diseases has been, and continues to be, an important component of controlling the spread of these diseases. For example, measles remains a critical public health issue for humans, resulting in over one million deaths per year globally. Vaccination against measles is one of the most cost-effective public health measures available to control the spread of measles, and global eradication of the disease is technically feasible using current vaccinations. A global eradication campaign is presently under consideration by the World Health Organization. Unlike past and ongoing eradication campaigns for smallpox and polio, however, a simple and low-cost vaccine administration technique is not presently available for measles. Current practice remains injection using a hypodermic syringe.
Hypodermic syringe methods of vaccination have numerous drawbacks, including the need for skilled personnel, risk of blood-borne disease, high cost, patient aversion to injection and the need to safely dispose of large quantities of needles and syringes. For a measles eradication campaign on a global scale, use of conventional needles and syringes is generally considered impractical. Streamlined techniques utilizing alternatives to hypodermic syringes, such as jet injectors, are necessary for safe and cost-effective mass vaccination campaigns.
Another issue regarding measles vaccination lies in reconstituting the vaccine. Current vaccine administration techniques require reconstitution of the vaccine by drawing a sterile diluent from a sealed vial via needle and syringe and injecting the diluent into another sealed vial containing lyophilized vaccine. The vial containing the diluent and lyophilate is then shaken to mix the diluent and lyophilate and complete the reconstitution. Thus, even if needle-free administration of the vaccine is subsequently used, the reconstitution process requires the use of needles and syringes, providing an opportunity for contamination of the reconstituted vaccine by reuse of dirty diluent-injection needles, the need to dispose of used diluent needles and syringes, a chance for use of the wrong diluent, occasion for measurement errors in obtaining proper dilution and the possibility of needle stick injuries by less-skilled, fatigued or distracted personnel. Moreover, the use of separate supply vials for vaccine and diluent requires multiple sterile containers to be ordered, transported, inventoried, coordinated and monitored.
Jet injection of vaccines was used successfully for many years until concerns regarding patient-to-patient contamination from multiple use injectors arose in the late 1980s and early 1990s. Substantial efforts are now underway to develop new injectors that utilize disposable fluid pathways to prevent contamination. Typically, these disposable pathways are in the form of cartridges that are similar in shape and functions to a conventional hypodermic syringe having a generally cylindrical barrel, or housing, and a plunger. Rapid movement of the plunger in the housing toward an orifice generates high pressures, and a jet of high-velocity liquid issues from the orifice and pierces the skin of a patient.
What is needed is an ejection system that may be used for, among other things, administering vaccines while reducing or eliminating the drawbacks of conventional vaccination systems, including the vaccination systems discussed above.